Thursday, June 5, 2014
Hardware support for integer overflow trapping...
Hardware support for integer overflow trapping... Hear, hear! I've spent way too many hours of my life tracking down this type of bug – and it looks so easy to do away with!
California leads the way...
California leads the way ... in Republican gains? This is an epic flying-pig moment, and I'd be willing to bet you that Democratic strategists around the country are worried. Very worried. In the land where Democrats have complete control, where their policies romp freely over the citizenry's freedoms and pocketbooks, and where regulations are a major component of the very air they breath ... the Democrats lost ground. That's not supposed to happen, you know. Them there citizens appear to be getting a mite uppity!
Did low fat diets promote obesity?
Did low fat diets promote obesity? This book makes that claim, and at least one reviewer finds that it makes a plausible case...
The rollback of my ignorance, however slight, is sufficient to complete my morning...
The rollback of my ignorance, however slight, is sufficient to complete my morning... Friend and former colleague Doug W. (who actually understands the math that I dabble at the edges of) explains the “magic” p^2 - 1 factoid. He writes:
You had a blog entry yesterday about the fact that p**2 - 1 is divisible by 24 for any prime p > 3. It's actually very simple to derive the result. Assume that p is an odd number, not divisible by 3 (in the problem as stated, we know that p isn't divisible by 3, since p is prime :-).He's right, it is simple! Assuming, that is, you're facile enough with math to be able to work it out :)
Now, p**2 - 1 = (p+1)(p-1). Note that these two factors are consecutive even integers. Thus, exactly one of them must be multiple of 4, so when you multiply the two factors together you get a multiple of 8. That is, we know that p-1 is either of the form 4k or 4k+2, in which case p+1 would be of the form 4k+2 or 4k+4, respectively. So the product is either of the form 4k*(4k+2) or (4k+2)(4k+4), each of which is divisible by 8.
Further, since p is not divisible by 3, and since in any three consecutive integers there is exactly one multiple of 3, then either (p+1) or (p-1) must be divisible by 3. Thus, the overall product is a multiple of 8*3 (i.e., 24).
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